In a statement to ITV, Cities of London and Westminster MP Mr Field said: “In the confusion many guests understandably felt threatened and when one protester rushed past me towards the top table I instinctively reacted.

“There was no security present and I was for a split-second genuinely worried she might have been armed.

“As a result I grasped the intruder firmly in order to remove her from the room as swiftly as possible.”

He added that he “deeply” regretted the incident and would co-operate fully with a Cabinet Office investigation.

Mr Field was a minister in Jeremy Hunt’s team at the Foreign Office and also supported him for the Tory leadership.

Mr Hunt told the BBC: “Mark has issued a full and unreserved apology. He recognises that what happened was an over-reaction.”

A climate change activist from Greenpeace who interrupted the speech (Simon Dawson/PA)

Sir Peter, whose wife Virginia – now Baroness Bottomley – was assaulted while health secretary, said if a police officer had done what Mr Field did, “would there have been a fuss? The answer is no”.

But shadow women and equalities secretary Dawn Butler described the incident as “horrific” and said “so much violence does not seem justified”.

Senior captains of industry and top City executives were among the invited guests hearing speeches by Mr Hammond and Bank of England governor Mark Carney.

A City of London Police spokesman said: “We have received a small number of third-party reports of an assault taking place at the event. These reports are being looked into by police.”

The City of London Corporation said it was investigating the breach of security at Mansion House and “will be reviewing arrangements for future events”.

The UK remains committed to helping women all over the world to feel safe and protected in the work they do, so they can speak freely and be part of the change we all want. My remarks at the Westminster Hall Debate on Women Human Rights Defenders. https://t.co/fmQMtXSTgV